Managed bumble bees increase flower visitation but not fruit weight in polytunnel strawberry crops

Animal-mediated pollination is essential for the production and quality of fruits and seeds of many crops consumed by humans. However, crop pollination services might be compromised when wild pollinators are scarce. Managed pollinators are commonly used in crops to supplement such services with the assumption that they will enhance crop yield. However, information on the spatiotemporal pollinator-dependence of crops is still limited. We assessed the contribution of commercial bumble bee colonies compared to the available pollinator community on strawberry (‘Fortuna’ variety) flower visitation and strawberry quality across a landscape gradient of agricultural intensification (i.e. polytunnel berry crop cover). We used colonies of bumble bees in winter and in spring, i.e. when few and most wild pollinators are in their flight period, respectively. The placement of colonies increased visits of bumble bees to strawberry flowers, especially in winter. The use of bumble bee colonies did not affect flower visitation by other insects, mainly honey bees, hoverflies and other Diptera. Flower visitation by both honey bees and wild insects did not vary between seasons and was unrelated to the landscape gradient of berry crop cover. Strawberries were of the highest quality (i.e. weight) when insect-mediated pollination was allowed, and their quality was positively related to wild flower visitors in winter but not in spring. However, increased visits to strawberry flowers by managed bumble bees and honey bees had no effect on strawberry weight. Our results suggest that the pollination services producing high quality strawberry fruits are provided by the flower visitor community present in the study region without the need to use managed bumble bees.     

Proximity to wildflower strips did not boost crop pollination on small,diversified farms harboring diverse wild bees

The yield of many agricultural crops depends on pollination services provided by wild and managed bees, many of which are experiencing declines due to factors such as reductions in floral resources. Thus, improving pollinator habitat on farmlands using management strategies like planting wildflower strips is vital for wild bee conservation and sustainable crop pollination. Yet, few studies have examined whether and at what spatial scales wildflower strips enhance crop pollination and yields, and most research has been conducted in large-scale commercial agriculture. Therefore, we investigated the effects of wildflower strips on crop pollination on small, diversified farms (i.e., those growing a variety of crop species) where wild bee diversity and abundance is predicted to be comparatively high. Over three years, on four diversified farms in Montana USA, we tested the hypothesis that distance (20, 60, and 180 m) of crops from native perennial wildflower strips planted alongside crop fields affected wild bee visitation, pollination, and yields of squash and sunflower crop plants. We found that distance to wildflower strips did not affect bee visitation or pollination in crops. Squash yield was pollen-limited in the growing season prior to wildflower strip establishment, and in one of the two years after wildflower strip establishment, but proximity to wildflower strips did not influence the magnitude of pollen limitation. Sunflower seed production was not pollen-limited in any year. Our findings demonstrate that even on diverse farms with wildflower strips and a demonstrated high diversity of bees, some crops do not necessarily receive maximum pollination, regardless of distance from the wildflower strips. However, the value of wildflower strips for supporting wild bee diversity, and other ecological or economic benefits, needs consideration for a full understanding of this pollinator habitat management strategy.     

Native flower strips increase visitation by non-bee insects to avocado flowers and promote yield

Pollination is an essential ecosystem service for pollinator-dependent crops and plant communities. Apis mellifera L. is by far the most commonly used species to obtain this service in agriculture. However, there is growing evidence of the importance for crop yields of the service provided by wild bees and non-bee insect pollinators. Establishing flower resources in agricultural landscapes is a management practice that can increase insect pollinator populations and improve crop yields. We established perennial native flower strips (NFS) in four avocado orchards in central Chile during autumn 2017. We monitored flower visitors and counted newly formed fruits in avocados near and far from NFS in spring 2019, to assess flower visitor groups, flower visitation rates and fruit numbers. Only A. mellifera visited avocado flowers within bees, whereas both the managed A. mellifera and wild bees were the main visitors to the NFS. NFS increased visitation rates to adjacent avocado of flies, and with a trend for the sum of all non-managed flower visitors (i.e. excluding A. mellifera). However, there were no differences in the rates of A. mellifera visitation to avocados near and far from NFS. Avocado fruit numbers were higher among avocados near NFS than among those farther away. This difference could be due to better pollination by the increased visits to avocado flowers by flies or other wild insects. Therefore, NFS could contribute to crop fruit number, as well as conservation of native flora, wild bees and non-bee pollinators on fruit farms in the “Central Chile” biodiversity hotspot.     

Seasonal complementary in pollinators of soft-fruit crops

Understanding the relative contributions of wild and managed pollinators, and the functional contributions made by a diverse pollinator community, is essential to the maintenance of yields in the 75% of our crops that benefit from insect pollination. We describe a field study and pollinator exclusion experiments conducted on two soft-fruit crops in a system with both wild and managed pollinators. We test whether fruit quality and quantity is limited by pollination, and whether different pollinating insects respond differently to varying weather conditions. Both strawberries and raspberries produced fewer marketable fruits when insects were excluded, demonstrating dependence on insect pollinators. Raspberries had a short flowering season which coincided with peak abundance of bees, and attracted many bees per flower. In contrast, strawberries had a much longer flowering season and appeared to be much less attractive to pollinators, so that ensuring adequate pollination is likely to be more challenging. The proportion of high-quality strawberries was positively related to pollinator abundance, suggesting that yield was limited by inadequate pollination on some farms. The relative abundance of different pollinator taxa visiting strawberries changed markedly through the season, demonstrating seasonal complementarity. Insect visitors responded differently to changing weather conditions suggesting that diversity can reduce the risk of pollination service shortfalls. For example, flies visited the crop flowers in poor weather and at the end of the flowering season when other pollinators were scarce, and so may provide a unique functional contribution. Understanding how differences between pollinator groups can enhance pollination services to crops strengthens the case for multiple species management. We provide evidence for the link between increased diversity and function in real crop systems, highlighting the risks of replacing all pollinators with managed alternatives.     

Impacts of the use of nonnative commercial bumble bees for pollinator supplementation in raspberry

Evidence for pollinator declines has led to concern that inadequate pollination services may limit crop yields. The global trade in commercial bumble bee (Bombus spp.) colonies provides pollination services for both glasshouse and open-field crops. For example, in the United Kingdom, commercial colonies of nonnative subspecies of the bumble bee Bombus terrestris L. imported from mainland Europe are widely used for the pollination of raspberries, Rubus idaeus L. The extent to which these commercial colonies supplement the services provided by wild pollinators has not been formally quantified and the impact of commercial bumble bees on native bees visiting the crop is unknown. Here, the impacts of allowing commercially available bumble bee colonies to forage on raspberry canes are assessed in terms of the yield of marketable fruit produced and the pollinator communities found foraging on raspberry flowers. No differences were found in the abundance, diversity, or composition of social bee species observed visiting raspberry flowers when commercial bumble bees were deployed compared with when they were absent. However, weight of marketable raspberries produced increased when commercial bees were present, indicating that wild pollinator services alone are inadequate for attaining maximum yields. The findings of the study suggests that proportional yield increases associated with deployment of commercial colonies may be small, but that nevertheless, investment in commercial colonies for raspberry pollination could produce very significant increases in net profit for the grower. Given potential environmental risks associated with the importation of nonnative bumble bees, the development of alternative solutions to the pollination deficit in raspberry crops in the United Kingdom may be beneficial.     

Small wild bee abundance declines with distance into strawberry crops regardless of field margin habitat

The preservation of pollinator habitat on croplands in the form of hedgerows, wildflower strips, and natural and semi-natural areas can help maintain and enhance wild bee populations in agricultural landscapes. However, there have been few comparisons of the effectiveness of different types of field-margin pollinator habitat in maintaining bee diversity and pollination of the focal crops. We compared wild bee abundance, species richness and community composition between strawberry crops bordered by hedgerows, and those bordered by larger expanses of natural land (forests). Strawberry is an ideal crop in which to investigate pollinator export from field margins as the rows are covered with straw, which reduces habitat for ground-nesting bees within the crop; thus, most wild pollinators need to enter the crop from the margins. We sampled bees in six strawberry fields with hedgerow margins and six strawberry fields with forested margins of at least 200 m in length, using a paired design. We examined strawberry pollen deposition at regular intervals into the fields, and the magnitude of pollinator export from the field margins towards the centre of the crops. We found that bees as a group were no more species-rich or abundant in crops bordered by forests than in crops bordered by hedgerows, although large-bodied bees were more abundant in the former than the latter. Regardless of field-margin type, we found that small wild bee abundance declined significantly from the edge to the centre of the crop, but honey bee (Apis mellifera L.) and large-bodied bee abundance did not. Strawberry pollen deposition also did not decline with distance into the crop. Although previous work indicates that small wild bees are more effective (yield-increasing) pollinators of strawberry on a per-visit basis, their limited foraging ranges suggest they may only pollinate areas near the crop margins, given typical field sizes in our area.     

Crop management affects pollinator attractiveness and visitation in oilseed rape

Ecological intensification of agriculture implies managing ecological processes to improve performance of agricultural systems. However, impacts on relevant ecological functions such as insect pollination from other crop management factors are poorly explored. Pest insects and crop resources such as water availability can directly affect crop yields, but it is unknown if there are indirect effects through effects on insect pollination. With a factorial experiment, we examined how irrigation and control of pollen beetles affected crop attractiveness and pollinator visitation in an open-pollinated spring oilseed rape cultivar. We studied how irrigation and pest control modified the production of flowers and nectar in oilseed rape, and if this in turn affected the flower-visitation of honey bees and bumble bees. Pest control increased the number of oilseed rape flowers by 69%, and the amount of nectar per flower with 36%, but for the latter only in non-irrigated plots. Furthermore, we found higher pollinator densities in plots with reduced pollen beetle densities. Pest control also reduced the number of non-legitimate flower visits, suggesting higher pollination efficiency in plots with reduced pollen beetle densities. We show that crop management affects the value of mass-flowering crops as a resource for pollinating insects. Development of pest control tools that are harmless to pollinators could increase the value of flowering crops as food resources for pollinating insects.     

Contribution of native bees and Africanized honey bees (Hymenoptera:Apoidea) to Solanaceae crop pollination in tropical México

In the tropics the contribution of bees as pollinators of important economic indigenous crops remains largely undocumented. We studied the diversity of bee species visiting indigenous tomato (Solanum lycopersicon) and habanero pepper (Capsicum chinense) in subtropical Yucatán, México. The contribution of two native bees, Exomalopsis (E) and Augochloropsis (AG) was compared with that of the introduced Africanized Apis mellífera (HB) for pollinating unvisited flowers in both crops. Apis mellífera and stingless bees were dominant in habanero pepper but solitary bee species were important visitors of tomato. In spite of both crops being autogamic, there was a significant contribution of native bees for pollination of both tomato and habanero pepper. The comparison of fruit weight, number of seeds, and a pollination index based on the latter showed that E and AG were more effective pollinators compared to HB in both crops (ca. Spear’s index of ca. 0.7 vs. 0.35 respectively). In tomato, a further evaluation of the contribution to pollination provided by the three bee species was made using the rate of visits to flowers. Although E and AG were the most efficient pollinators at single flower visits in tomato, none of the three species (including HB) were able to provide single visits to all flowers per unit time to the crop. Our results underline the importance of maintaining diverse assemblages and abundant populations of bee species that can synergically contribute to the productivity of tomato and hot pepper in the Neotropics.     

Pollinator population size and pollination ecosystem service responses to enhancing floral and nesting resources

Modeling pollination ecosystem services requires a spatially explicit, process‐based approach because they depend on both the behavioral responses of pollinators to the amount and spatial arrangement of habitat and on the within‐ and between‐season dynamics of pollinator populations in response to land use. We describe a novel pollinator model predicting flower visitation rates by wild central‐place foragers (e.g., nesting bees) in spatially explicit landscapes. The model goes beyond existing approaches by: (1) integrating preferential use of more rewarding floral and nesting resources; (2) considering population growth over time; (3) allowing different dispersal distances for workers and reproductives; (4) providing visitation rates for use in crop pollination models. We use the model to estimate the effect of establishing grassy field margins offering nesting resources and a low quantity of flower resources, and/or late‐flowering flower strips offering no nesting resources but abundant flowers, on bumble bee populations and visitation rates to flowers in landscapes that differ in amounts of linear seminatural habitats and early mass‐flowering crops. Flower strips were three times more effective in increasing pollinator populations and visitation rates than field margins, and this effect increased over time. Late‐blooming flower strips increased early‐season visitation rates, but decreased visitation rates in other late‐season flowers. Increases in population size over time in response to flower strips and amounts of linear seminatural habitats reduced this apparent competition for pollinators. Our spatially explicit, process‐based model generates emergent patterns reflecting empirical observations, such that adding flower resources may have contrasting short‐ and long‐term effects due to apparent competition for pollinators and pollinator population size increase. It allows exploring these effects and comparing effect sizes in ways not possible with other existing models. Future applications include species comparisons, analysis of the sensitivity of predictions to life‐history traits, as well as large‐scale management intervention and policy assessment.     

Co-flowering plants support diverse pollinator populations and facilitate pollinator visitation to sweet cherry crops

Many food crops depend on animal pollination to set fruit. In light of pollinator declines there is growing recognition of the need for agro-ecosystems that can sustain wild pollinator populations, ensuring fruit production and pollinator conservation into the future. One method of supporting resident wild pollinator populations within agricultural landscapes is to encourage and maintain floral diversity. However, pollinator visitation to crop plants can be affected either positively (facilitation) or negatively (competition) by the presence of co-flowering plants. The strength and direction of the facilitative/competitive relationship is driven by multiple factors, including floral abundance and the degree of overlap in pollinator visitation networks. We sought to determine how plant-pollinator networks, within and surrounding sweet cherry (Prunus avium) orchards, change across key time points during the cherry flowering season, in three growing regions in Australia. We found significant overlap in the suite of flower visitors, with seven taxa (including native bees, flies, hoverflies and introduced honey bees, Apis mellifera) observed visiting cherry and other co-flowering species within the orchard and/or the wider surrounding matrix. We found evidence of pollinator facilitation with significantly more total cherry flower visits with increasing percent cover of co-flowering plants within the wider landscape matrix and increased visitation to cherry by honey bees with increasing co-flowering plant richness within the orchard. During the cherry flowering period there was a significant positive relationship between pollinator richness on cherry and pollinator richness on co-flowering plants within the orchard and the area of native vegetation surrounding orchards. Outside of the crop flowering season, co-flowering plants within the orchard and wider landscape matrix supported the same pollinator taxa that were recorded visiting cherry when the crop was flowering. This shows wild plants help support the pollinators important to crop pollination, outside of the crop flowering season, highlighting the role of co-flowering plants within pollinator-dependent cropping systems.     

Fruit set in perennial vetch (Vicia unijuga): reproductive system and insect role in pollination

Perennial vetch (Vicia unijuga) is a wild plant found in parts of East Asia and potentially valuable as a forage species for more extreme environments. Information on its reproductive system and pollination biology is needed for progress in domestication of the species. We characterized the reproductive system of perennial vetch as facultative xenogamy (i.e. it is largely cross‐pollinated by insects but is also self‐compatible and can self‐pollinate). There was no significant difference (P > 0.05) in the fruit set ratio between insect cross‐pollination and artificial cross‐pollination at the seed maturation stage, but natural self‐pollination was inefficient. In our study conducted on the Tibetan plateau, eight insect species (especially certain bumble bees) are identified as potential pollinators, and four other insect species belonging to the Lepidoptera and Diptera visited flowers but are unlikely to be pollinators. The flower visitation rate of wild bumble bees was 1.6–3.3 times higher than domestic honeybees, with Bombus lepidus having the highest visitation rate of 15.7 florets/min. The diurnal floret opening rhythm of perennial vetch was synchronized with diurnal activity of potential pollinators. Optimal pollination of perennial vetch would likely be achieved using wild bees, as they have behaviour characteristics and flower tripping ability necessary, and are present in sufficient numbers to be efficient pollinators of this crop. However, even with sufficiency of pollination, there remains a fundamental problem with low fruit set which requires further investigation from a plant biology perspective.     

Nectar robbery by bees Xylocopa virginica and Apis mellifera contributes to the pollination of rabbiteye blueberry

Honey bees, Apis mellifera L., probe for nectar from robbery slits previously made by male carpenter bees, Xylocopa virginica (L.), at the flowers of rabbiteye blueberry, Vaccinium ashei Reade. This relationship between primary nectar robbers (carpenter bees) and secondary nectar thieves (honey bees) is poorly understood but seemingly unfavorable for V. ashei pollination. We designed two studies to measure the impact of nectar robbers on V. ashei pollination. First, counting the amount of pollen on stigmas (stigmatic pollen loading) showed that nectar robbers delivered fewer blueberry tetrads per stigma after single floral visits than did our benchmark pollinator, the southeastern blueberry bee, Habropoda laboriosa (F.), a recognized effective pollinator of blueberries. Increasing numbers of floral visits by carpenter bee and honey bee robbers yielded larger stigmatic loads. As few as three robbery visits were equivalent to one legitimate visit by a pollen-collecting H. laboriosa female. More than three robbery visits per flower slightly depressed stigmatic pollen loads. In our second study, a survey of 10 commercial blueberry farms demonstrated that corolla slitting by carpenter bees (i.e., robbery) has no appreciable affect on overall V. ashei fruit set. Our observations demonstrate male carpenter bees are benign or even potentially beneficial floral visitors of V ashei. Their robbery of blueberry flowers in the southeast may attract more honey bee pollinators to the crop.     

Bumble bee abundance and richness improves honey bee pollination behaviour in sweet cherry

Pollination service in agricultural crops increases significantly with pollinator diversity and wild pollinator abundance. Differences in the foraging behaviour of pollinating insects are one of the reasons why pollinator diversity and abundance enhances crop pollination. Here, we focused on the foraging behaviour of honey bees and bumble bees in sweet cherry orchards. In addition, we studied the influence of bee diversity and abundance on the foraging behaviour of honey bees and bumble bees. Honey bees were found to visit fewer flowers than bumble bees. Bumble bees also showed a higher probability of changing trees between rows than honey bees. Both visitation rate and probability of row changes of honey bees increased with bumble bee diversity and with bumble bee abundance. We also found that the probability of row changes of honey bees increased with increasing bumble bee abundance. These effects of bumble bee richness and abundance on the pollination behaviour of honey bees can improve the pollination performance of honey bees in crops that depend on cross pollination. Our results highlight the higher pollination performance of bumble bees and the facilitative effect of wild pollinators to crop pollination.     

Isolation from natural habitat reduces yield and quality of passion fruit

• Loss and fragmentation of native vegetation negatively affect crop pollinators and productivity of several crop species. The yellow passion fruit is an excellent model to investigate this issue, because its main pollinators are sensitive to deforestation. Seasonality also influences fruit set of crop species that are pollinated by bees. Climate determines plant flowering patterns and consequently affects pollinator activity. Little is known on effects of pollinators on crop quality in general, and particularly of many tropical fruits that have multiple fruiting seasons throughout the year, such as passion fruit. Our hypothesis is that the distance to the native vegetation and climate seasonality affect the pollination and fruit production of cultivated, hermaphrodite, self‐incompatible, protandrous species that depend on large‐sized bees to set fruit.
• We observed flowers of the yellow passion fruit in eight areas at different distances (600–4,000 m) from a dry seasonal forest (Caatinga). We compared the frequency of the main floral visitor (pollinators and robbers) visits and fruit set among areas at the beginning and end of the dry and rainy seasons.
• Xylocopa species were pollinators, and Apis mellifera, Trigona spinipes and a hummingbird were robbers. Xylocopa visits diminished with increasing distance to native remnants, converse to what was observed for the robbers at the beginning of the dry season. Fruit set was higher at the beginning of the dry season. The distance to the forest affected quality of fruits in terms of length, diameter and skin thickness, which all decreased with increase in remnant distance.
• Our results show that insect pollination is higher in the dry season, increasing profitability and reducing labour costs for the producer. Considering the influence of distance to native vegetation on pollination, robbery and fruit quality, our study reinforces the necessity for conservation of native vegetation remnants.

     

Influence of functional traits on foraging behaviour and pollination efficiency of wild social and solitary bees visiting coffee (Coffea canephora) flowers in Uganda

An on-farm pollination experiment was conducted during the June–August and November–February blooming seasons of 2007 to 2008, in 30 small-scale coffee fields characterised by different habitat and vegetation types. The study was conducted in order to determine the best pollinator groups for coffee in Uganda and to collect relevant field information and determine the pollination efficiency of different bee species. Results indicate that across blooming seasons, coffee flowers were visited by 24–36 bee species. Hypotrigona gribodoi was the most frequent flower visitor, comprising over 60% of 5941 bee-visits recorded. Foraging rate and pollination speed varied among bee species. Solitary bees foraged on more flowers than social bees, but they spent less time per flower visited. Solitary bees visited more coffee trees and fields, but deposited less pollen, whereas social bees visited less trees and coffee fields in the landscape, but deposited more pollen on flowers. Fruit set was of 87%, 64% and 0.9%, respectively, in hand-cross pollination, open pollination and controlled-pollination treatments. Fruit abortion due to self-pollination was insignificant in this study. There was variability in pollination efficiency of different bee species. Pollination efficiency varied more significantly with sociality than with other bee functional traits and was not significantly influenced by tongue length and bee body size. Single-flower visits by social and solitary bees resulted in 89.7% and 68.14% fruit set, respectively. The most efficient bee species was Meliponula ferruginea (98.3%) followed by Meliponula nebulata (97.1%). Thus, very good pollinator species were wild social bees (mainly stingless bees) as opposed to honeybees and solitary bees that were previously reported to be the best pollinators of coffee in Panama and Indonesia. Morphological and anatomical characteristics of the bee pollen storage features may explain the difference in foraging behaviour activities and in pollination efficiency of social and solitary afrotropical bee species visiting lowland coffee in Uganda. In addition, pollination efficiency was influenced by land-use intensity, field management systems and habitat types found in the immediate surroundings of coffee fields, but not by coffee field size, coffee genotypes and mass blooming wild vegetation. It is recommended to farmers to adopt pollinator-friendly conservation and farming practices such as keeping an uncultivated portion (25%–30%) of their farms as pollinator reservoirs, protecting semi-natural habitats found in the vicinity of coffee fields, as well as promoting high on-farm tree cover to benefit a functionally diverse pollinator community.     

Pollination Services Provided by Bees in Pumpkin Fields Supplemented with Either Apis mellifera or Bombus impatiens or Not Supplemented

Pollinators provide an important service in many crops. Managed honey bees (Apis mellifera L.) are used to supplement pollination services provided by wild bees with the assumption that they will enhance pollination, fruit set and crop yield beyond the levels provided by the wild bees. Recent declines in managed honey bee populations have stimulated interest in finding alternative managed pollinators to service crops. In the eastern U.S., managed hives of the native common eastern bumble bee (Bombus impatiens Cresson) may be an excellent choice. To examine this issue, a comprehensive 2-yr study was conducted to compare fruit yield and bee visits to flowers in pumpkin (Cucurbita pepo L.) fields that were either supplemented with A. mellifera hives, B. impatiens hives or were not supplemented. We compared pumpkin yield, A. mellifera flower visitation frequency and B. impatiens flower visitation frequency between treatments. Results indicated that supplementing pumpkin fields with either A. mellifera or B. impatiens hives did not increase their visitation to pumpkin flowers or fruit yield compared with those that were not supplemented. Next, the relationship between frequency of pumpkin flower visitation by the most prominent bee species (Peponapis pruinosa (Say), B. impatiens and A. mellifera) and fruit yield was determined across all pumpkin fields sampled. Fruit yield increased as the frequency of flower visits by A. mellifera and B. impatiens increased in 2011 and 2012, respectively. These results suggest that supplementation with managed bees may not improve pumpkin production and that A. mellifera and B. impatiens are important pollinators of pumpkin in our system.     

Pollination efficiency and foraging behaviour of honey bees and non‐Apis bees to sweet cherry

1. Crop pollination generally increases with pollinator diversity and wild pollinator visitation. To optimize crop pollination, it is necessary to investigate the pollination contribution of different pollinator species. In the present study, we examined this contribution of honey bees and non‐Apis bees (bumble bees, mason bees and other solitary bees) in sweet cherry.
2. We assessed the pollination efficiency (fruit set of flowers receiving only one visit) and foraging behaviour (flower visitation rate, probability of tree change, probability of row change and contact with the stigma) of honey bees and different types of non‐Apis bees.
3. Single visit pollination efficiency on sweet cherry was higher for both mason bees and solitary bees compared with bumble bees and honey bees. The different measures of foraging behaviour were variable among non‐Apis bees and honey bees. Adding to their high single visit efficiency, mason bees also visited significantly more flower per minute, and they had a high probability of tree change and a high probability to contact the stigma.
4. The results of the present study highlight the higher pollination performance of solitary bees and especially mason bees compared with bumble bees and honey bees. Management to support species with high pollination efficiency and effective foraging behaviour will promote crop pollination.

     

Does the morphological fit between flowers and pollinators affect pollen deposition? An experimental test in a buzz‐pollinated species with anther dimorphism

Some pollination systems, such as buzz‐pollination, are associated with floral morphologies that require a close physical interaction between floral sexual organs and insect visitors. In these systems, a pollinator's size relative to the flower may be an important feature determining whether the visitor touches both male and female sexual organs and thus transfers pollen between plants efficiently. To date, few studies have addressed whether in fact the “fit” between flower and pollinator influences pollen transfer, particularly among buzz‐pollinated species. Here we use Solanum rostratum, a buzz‐pollinated plant with dimorphic anthers and mirror‐image flowers, to investigate whether the morphological fit between the pollinator's body and floral morphology influences pollen deposition. We hypothesized that when the size of the pollinator matches the separation between the sexual organs in a flower, more pollen should be transferred to the stigma than when the visitor is either too small or too big relative to the flower. To test this hypothesis, we exposed flowers of S. rostratum with varying levels of separation between sexual organs, to bumblebees (Bombus terrestris) of different sizes. We recorded the number of visits received, pollen deposition, and fruit and seed production. We found higher pollen deposition when bees were the same size or bigger than the separation between anther and stigma within a flower. We found a similar, but not statistically significant pattern for fruit set. In contrast, seed set was more likely to occur when the size of the flower exceeded the size of the bee, suggesting that other postpollination processes may be important in translating pollen receipt to seed set. Our results suggest that the fit between flower and pollinator significantly influences pollen deposition in this buzz‐pollinated species. We speculate that in buzz‐pollinated species where floral morphology and pollinators interact closely, variation in the visitor's size may determine whether it acts mainly as a pollinator or as a pollen thief (i.e., removing pollen rewards but contributing little to pollen deposition and fertilization).     

Limited Fruit Production in Hancornia speciosa (Apocynaceae) and Pollination by Nocturnal and Diurnal Insects1

Frequency and efficiency of pollinator visits strongly influence the reproductive success of self‐incompatible plants. We investigated the breeding and pollination systems of Hancornia speciosa, a small tree that produces fleshy berries used in the Brazilian fruit industry. Observation and experiments were carried out in Northeastern Brazil. Thirty‐three species of the visitor were recorded. Hawkmoths (Sphingidae), bees (Euglossini and Centridini), and butterflies (Nymphalidae and Hesperiidae) with long mouth parts were effective pollinators of H. speciosa. Access to nectar, the only reward for flower visitors, is determined by corolla tube length. Nylon threads of various diameters and dried mouth parts from a number of flower visitors were used in experiments to simulate flower visits. The number of pollen grains removed during such simulated visits showed no significant difference. Although xenogamic, H. speciosa presented a low pollen/ovule ratio (77). This might be related to the high efficiency of its pollination mechanism. Flowers of H. speciosa had 76 ovules on average. Seed set varied from 1 to 25, indicating that individual flowers received different amounts of outcross‐pollen. Fruit production of hand cross‐pollinated flowers increased by 90 percent when compared to natural pollination, suggesting pollinator limitation of H. speciosa.     

Integrated crop pollination to buffer spatial and temporal variability in pollinator activity

Insect pollination improves the yield and quality of many crops, yet there is increasing evidence of insufficient insect pollinators limiting crop production. Effective Integrated Crop Pollination (ICP) involves adaptable, targeted and cost-effective management of crop pollination and encourages the use of both wild and managed pollinators where appropriate. In this study we investigate how the addition of honeybee hives affects the community of insects visiting oilseed rape, and if hive number and location affect pollinator foraging and oilseed rape pollination in order to provide evidence for effective ICP. We found that introducing hives increased overall flower visitor numbers and altered the pollinator community, which became dominated by honeybees. Furthermore a greater number of hives did not increase bee numbers significantly but did result in honeybees foraging further into fields. The timing of surveys and proximity to the field edge influenced different pollinators in different ways and represents an example of spatial and temporal complementarity. For example dipteran flower visitor numbers declined away from the field edge whereas honeybees peaked at intermediate distances into the field. Furthermore, no significant effects of survey round on wild bees overall was observed but honeybee numbers were relatively lower during peak flowering and dipteran abundance was greater in later survey rounds. Thus combining diverse wild pollinators and managed species for crop pollination buffers spatial and temporal variation in flower visitation. However we found no effect of insect pollination on seed set or yield of oilseed rape in our trial, highlighting the critical need to understand crop demand for insect pollination before investments are made in managing pollination services.